Sun Cluster Concepts Guide for Solaris OS

Disk Path Monitoring

The current release of Sun Cluster software supports disk path monitoring (DPM). This section provides conceptual information about DPM, the DPM daemon, and administration tools that you use to monitor disk paths. Refer to Sun Cluster System Administration Guide for Solaris OS for procedural information about how to monitor, unmonitor, and check the status of disk paths.

DPM Overview

DPM improves the overall reliability of failover and switchover by monitoring secondary disk path availability. Use the cldevice command to verify the availability of the disk path that is used by a resource before the resource is switched. Options that are provided with the cldevice command enable you to monitor disk paths to a single Solaris host or to all Solaris hosts in the cluster. See the cldevice(1CL) man page for more information about command-line options.

The following table describes the default location for installation of DPM components.





Command-line interface 


Daemon status file (created at runtime) 


A multithreaded DPM daemon runs on each host. The DPM daemon (scdpmd) is started by an rc.d script when a host boots. If a problem occurs, the daemon is managed by pmfd and restarts automatically. The following list describes how the scdpmd works on initial startup.

Note –

At startup, the status for each disk path is initialized to UNKNOWN.

  1. The DPM daemon gathers disk path and node name information from the previous status file or from the CCR database. See Cluster Configuration Repository (CCR) for more information about the CCR. After a DPM daemon is started, you can force the daemon to read the list of monitored disks from a specified file name.

  2. The DPM daemon initializes the communication interface to respond to requests from components that are external to the daemon, such as the command-line interface.

  3. The DPM daemon pings each disk path in the monitored list every 10 minutes by using scsi_inquiry commands. Each entry is locked to prevent the communication interface access to the content of an entry that is being modified.

  4. The DPM daemon notifies the Sun Cluster Event Framework and logs the new status of the path through the UNIX syslogd command. See the syslogd(1M) man page.

Note –

All errors that are related to the daemon are reported by pmfd. All the functions from the API return 0 on success and -1 for any failure.

The DPM daemon monitors the availability of the logical path that is visible through multipath drivers such as Solaris I/O multipathing (MPxIO), which was formerly named Sun StorEdge Traffic Manager, Sun StorEdge 9900 Dynamic Link Manager, and EMC PowerPath. The individual physical paths that are managed by these drivers are not monitored because the multipath driver masks individual failures from the DPM daemon.

Monitoring Disk Paths

This section describes two methods for monitoring disk paths in your cluster. The first method is provided by the cldevice command. Use this command to monitor, unmonitor, or display the status of disk paths in your cluster. You can also use this command to print a list of faulted disks and to monitor disk paths from a file. See the cldevice(1CL) man page.

The second method for monitoring disk paths in your cluster is provided by the Sun Cluster Manager graphical user interface (GUI). Sun Cluster Manager provides a topological view of the monitored disk paths in your cluster. The view is updated every 10 minutes to provide information about the number of failed pings. Use the information that is provided by the Sun Cluster Manager GUI in conjunction with the cldevice command to administer disk paths. See Chapter 12, Administering Sun Cluster With the Graphical User Interfaces, in Sun Cluster System Administration Guide for Solaris OS for information about Sun Cluster Manager.

Using the cldevice Command to Monitor and Administer Disk Paths

The cldevice command enables you to perform the following tasks:

Issue the cldevice command with the disk path argument from any active node to perform DPM administration tasks on the cluster. The disk path argument consists of a node name and a disk name. The node name is not required. If you do not specify a node name, all nodes are affected by default. The following table describes naming conventions for the disk path.

Note –

Always specify a global disk path name rather than a UNIX disk path name because a global disk path name is consistent throughout a cluster. A UNIX disk path name is not. For example, the disk path name can be c1t0d0 on one node and c2t0d0 on another node. To determine a global disk path name for a device that is connected to a node, use the cldevice list command before issuing DPM commands. See the cldevice(1CL) man page.

Table 3–3 Sample Disk Path Names

Name Type 

Sample Disk Path Name 


Global disk path  


Disk path d1 on the schost-1 node



Disk path d1 on all nodes in the cluster

UNIX disk path  


Disk path c0t0d0s0 on the schost-1 node



All disk paths on the schost-1 node

All disk paths 


All disk paths on all nodes of the cluster 

Using Sun Cluster Manager to Monitor Disk Paths

Sun Cluster Manager enables you to perform the following basic DPM administration tasks:

The Sun Cluster Manager online help provides procedural information about how to administer disk paths.

Using the clnode set Command to Manage Disk Path Failure

You use the clnode set command to enable and disable the automatic rebooting of a node when all monitored disk paths fail. You can also use Sun Cluster Manager to perform these tasks.